Many computer image, entertainment video, and video teleconferencing services require large-screen displays so that users can realize the maximal benefit and effectiveness of these services. A particular concern with large display screens, especially in residential environments, is the volume of living space encroached upon by the video display screen. A solution to this problem would be a true large-screen flat display having negligible depth that can be hung inconspicuously on the wall. This solution, although under research for many years, remains decidedly elusive.
Another approach is the use of rear-projection television (RPTV) receivers which are currently available in the consumer market. RPTV receivers provide reasonable brightness and are somewhat tolerant to ambient room light while still producing good contrast. However, these receivers are large in size, and significantly encroach on the volume of living space, especially for enhanced quality video formats.
Another approach to large screen video displays, which minimizes the apparent loss of living space, is front projection systems. A front projection system displays an image by directing the projected light from the projector onto a projection screen which diffusely reflects the light back into the viewing area.
The most pronounced advantage of front projection systems is that the video projection screen, which is a thin, wall-mountable unit, is separate from the video projector, which can be mounted in various positions within the room, thus lessening the apparent loss of living space. Front projection systems will be even more desirable as alternate video projector technologies such as liquid crystal, deformable media or laser projection technologies are employed. By employing these technologies, the projector will shrink to an insignificant size, and the entire arrangement will approach the effectiveness and level of user comfort of a single flat-screen video display. Furthermore, in shrinking the size of the projector, it can be suspended conveniently from the ceiling of the viewing room for maximized living space and with the additional advantage that people are somewhat less likely to block the projected light as they move about the viewing room.
A significant disadvantage of prior front projection systems is the need for a darkened room in order to achieve tolerable contrast. A darkened room is required since light from the projector as well as ambient room light is efficiently returned by the display system, thereby yielding poor contrast to the viewer. Under normal room lighting conditions, the picture quality of front projection systems is poor compared to rear projection systems. Therefore, persons skilled in the art have expressed a preference for rear projection video display systems, especially for home use. See for example, High Definition TV Rear Projector Using LCD Panels, Yokozawa et al., CH-3071-8/91/00000-0004, pgs. 4-7, IEEE, 1991.
Ideally, while watching the video imagery of a front projection video system, viewers do nothing else requiring lighted ambient conditions and are content in a darkened room. However, this is not the reality. While watching a video display, viewers may be engaged in other activities which require lighting. Examples of such activities are reading television program listings, denoting the time, conversing with other viewers, etc. Furthermore, during video teleconferencing sessions, illumination of the conferees is needed by the monitoring cameras.
An object of our invention is to provide a front projection video display system, which yields high contrast without requiring darkened ambient conditions and minimizes the encroachment on the volume of living space unlike conventional rear projection visual display systems.